Contact between glass containers will cause external surface damage to the glass containers in the form of abrasions, bruises and scratches and thereby result in a loss of tensile strength of the glass containers. In order to protect the glass containers from such surface damage, glass containers are generally provided with a protective coating, particularly on the body portion. Such protective coating is conventionally applied at the "hot" end of the glassware manufacture line, i.e., between the glass-forming machine and the annealing lehr. At the hot end the glassware retains sufficient heat of formation so that the glassware has a temperature above about 800.degree. F.
At the hot end the glass containers are either fume-coated or liquid spray coated with a protective coating of a composition of a metallic compound which is heat decomposable upon contact with the hot glass containers. Typical of such protective coating compositions containing a heat decomposable metallic compound are those containing a tin salt, such as stannous chloride and stannic chloride, and those containing a titanium compound, such as titanium tetrachloride and tetraisopropyl titanate, the usual metallic compound being stannic chloride. Upon contact of the heat decomposable metallic compound with the hot glass containers, the applied compound decomposes into a metallic oxide, such as, stannic oxide or titanium oxide. The metallic oxide coating protects the external surface of the glass containers against damage from abrasive contact and thereby improves the tensile strength and appearance of the glassware.
The heretofore used hot end glassware coating systems suffer from a number of disadvantages which include complexity and expense of installation, operation and control and deficiencies in performance.